The present invention relates to inverter type illumination lighting apparatus.
In an inverter type illumination apparatus, DC voltage obtained from commercial AC voltage is converted into a high-frequency AC voltage which in turn is applied to a discharge tube and in recent years, the inverter type illumination apparatus has been used widely. In this type of illumination apparatus, the discharge tube may be either a typical fluorescent lamp with filament or an electrodeless fluorescent lamp without filament operative to generate plasma by using the line of magnetic force emitted from an exciting coil. As well known, in the fluorescent lamp, mercury vapor in a discharge tube is excited to cause it to discharge ultraviolet rays which in turn are converted into visual light at a fluorescent material applied to the inner surface of the tube. A typical fluorescent lamp incorporating amalgam has main amalgam for setting the mercury vapor pressure during lighting to an optimum value and auxiliary amalgam for accelerating discharge of mercury immediately after lighting. In lighting based on the conventional copper/iron stabilizer incorporating a glow lamp, the filament is preheated while the glow lamp is in operation and the auxiliary amalgam provided to the electrode is heated to raise the mercury vapor pressure in the tube so as to improve rising of luminous flux. In the inverter type, however, instantaneous lighting is required and consequently, sufficient time for filament preheating cannot be assured, raising a problem that the mercury vapor pressure is low immediately after lighting or at low temperatures to delay rising of luminous flux.
As a conventional example of improvement in luminous flux rising in fluorescent lamps, a lighting apparatus disclosed in JP-A-11-37641 is known. In the lighting apparatus, a fluorescent lamp provided in a refrigerator is turned on/off by means of a control circuit of the lighting apparatus in accordance with open/close of a door. The control circuit is connected to a timer and the timer operable non-cooperatively with open/close of the door acts to turn on/off the fluorescent lamp at a predetermined hour or time. Through this, a phenomenon that the temperature of the fluorescent lamp continues to be low for a long time can be mitigated. In addition, overpower can be supplied to the fluorescent lamp for a predetermined time following start of lighting to accelerate mercury vaporization inside the tube to thereby improve rising of luminous flux.
In the prior art, however, when the lamp is turned on/off non-cooperatively with open/close of the door of the refrigerator, the predetermined time is set using the timer provided in the lighting apparatus. Further, even when overpower is supplied to the lamp for the predetermined time immediately after lighting, the time is set by the timer to control lighting. Disadvantageously, when the timer is provided to the lighting apparatus to perform lighting control as described above, the number of parts is increased to increase the circuit scale and raise costs.
An object of the invention is to provide an illumination lighting apparatus capable of improving the luminous flux immediately after lamp lighting or at low temperatures in a lighting apparatus for use with a discharge tube suitable for high-frequency operation.
According to one aspect of the invention, to accomplish the above object, an illumination lighting apparatus provided with an inverter for converting DC voltage generated by a power supply circuit into AC voltage to supply the AC voltage to a resonance load circuit comprises a control circuit for adjusting or regulating electric power supplied to the resonance load circuit in accordance with operating conditions of a discharge tube after initial lighting in which the discharge tube starts lighting following preheating.